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Calcium Compounds: Properties & Plant Use

Instructor: Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

Calcium is an alkaline metal and forms bonds with several monatomic ions and polyatomic ions. In this lesson, we will focus on four calcium compounds and how their properties affect plants.

Calcium in the Diet

Calcium is crucial for optimal health. Milk, cheese, and vegetables are excellent sources of calcium. But Where do cows, who produce milk, get the calcium that is in their milk? If you said, ''from plants'', you are correct! No wonder they always say ''eat your vegetables''!

Calcium is the third of six alkaline earth metals. It is very abundant in the soil and critical for plant growth. Human beings need calcium for bone growth and so do plants, but plants don't have bones. Plants need the calcium to produce strong cell walls, for proper cell functioning and to enable them to absorb nitrate from the soil. Nitrate is a polyatomic ion containing three oxygen atoms and a nitrogen atom, NO3 -1.

Calcium in the ground is mostly in sedimentary rocks and minerals. Calcium compounds are generally insoluble, which are unusable by plants without special help from microbes. Microbes are single cell organisms such as bacteria, protozoa, fungi, and various nematodes and grubs. All of these organisms need calcium too, but they have the ability to use calcium in solid form. The waste they excrete contains the calcium compound that plants can absorb.

Higher power microscope photograph of a nematode
nematode

Let's focus on four calcium compounds and how they affect plants: calcium oxide, calcium carbonate, calcium sulfate, and calcium nitrate.

Soil Acidity

In addition to providing the necessary calcium to the soil, calcium compounds are added to soil to lower the acidity of the soil. The measure of acidity is pH, which stands for ''potential hydrogen''. Acids contain free hydrogen ions. The pH range for optimum plant health depends on the species of plant so it is important to monitor and regulate it.

Soil becomes acidic naturally. Rainwater is slightly acidic, and it can wash away ions in the soil such as the alkali metals including potassium and sodium, and alkaline earth metals such as calcium and magnesium. Gases from the decomposition of organic material react with water in the soil generating acids such as carbonic acid, sulfuric acid, and nitric acid.

The minerals plants need are more soluble in less acidic soil because those microbes we talked about earlier are more active in soil that is less acidic. Also, higher acidity in the soil causes more aluminum availability, which has a detrimental affect on plants' roots ability to uptake water.

Acid Neutralizers

Calcium Oxide

To make soil less acidic quickly, calcium oxide (CaO), also known as quicklime, can be added. Calcium oxide reacts with water to form calcium hydroxide, which is a base. A base is the opposite of an acid, which is why the pH of the soil is raised to more neutral levels when a base reacts with an acid.

CaO (s) + H2 O (l) → Ca(OH)2 (aq)

  • (s) means solid
  • (l) means liquid
  • (aq) means aqueous (dissolved in water)

Calcium Carbonate

Calcium carbonate, (CaCO3) can also be added to the soil to raise the pH.

CaCO3 + H2 O (l) → Ca+2 (aq) + OH-1 (aq) + CO2 (g)

Spraying the fields with compounds to improve the soil, which benefits plant growth
spray

Nutrients and Soil Structure

Not only do plants need the appropriate pH level, they need special nutrients too. Two compounds can be added to the soil to to provide necessary sulfur and nitrate (NO3 -1).

Calcium Sulfate

Sulfur is important in the photosynthesis process and other cell functions. Calcium sulfate is CaSO4 and is used as a fertilizer. Peas, beans, onions, garlic, corn, cotton and alfalfa especially benefit from the the addition of calcium sulfate to the soil. It is soluble enough in water to give plants the ability to absorb it.

Calcium sulfate helps adjust pH and is also beneficial in regulating the structure of the soil. Soils tend to get compacted, which makes it difficult for plants' roots to grow. The calcium sulfate loosens the soil and causes clay particles to clump together. This allows air and water to penetrate the soil easier, which is called aeration.

Soil needs to be aerated, and contain nutrients for proper plant growth
dirt

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